The present invention relates to an apparatus for improving the quality of steel sections. The term "sections" should be understood as including, according to the present invention, I-beams, channels, angle irons, Tees, plates, large sheets, flat bars, and sheets, and generally any rolled section having at least one flat face.
The apparatus according to the invention may be employed to improve killed steels or semiskilled steels or rimming steels.
The main qualities required by the users in steel sections are, among others, as high as possible ultimate tensile stress, limit of elasticity, and impact strength for the grade of steel used, as well as satisfactory weldability, fatigue strength, and ductility for the intended use of the steel section.
To improve weldability and ductility of a steel it is necessary to decrease its carbon and manganese content, which in turn results in a decrease in its tensile strength. To remedy this inconvenience, the steel may be subjected to a suitable cooling process, preferably directly applied at the outlet of the rolling mill, which permits certain characteristics of the section to be improved to some extent.
Should such a cooling process result in an improvement deemed insufficient as far as properties of the sections are concerned, one may resort to other processes to complement the mere cooling action. Among such processes, reference should be made particularly to that which comprises adding dispersoidal elements (Nb, V) to refine the steel grains and to cause hardening of ferrite by precipitation of such elements. This procedure is surely effective but has the inconvenience of a cost which increases in proportion as one aims at a higher limit of elasticity; it is also the more expensive the larger the dimensions of the sections.
What is desired is a process which permits the above-mentioned inconveniences to be avoided without increasing to an unacceptable extent the carbon and manganese contents in the steel of the sections concerned which would otherwise result in detrimental effects on their weldability and impact strength at low temperature.